Sealing baths



SEALING BATHS Walter Glauser, Zollikon, Zurich, and Max Keller, Basel,Switzerland, assignors to J. R. Geigy A.-G., Basel, Switzerland, a Swisscorporation No Drawing. Application March 5, 1954, Serial No. 414,494

Claims priority, application Switzerland March 18, 1953 2 Qiaims. (Cl.204-) Generally the oxide coating of anodically oxidised aluminium issubmitted to a sealing process in order to close the pores. It is onlyafter this sealing that the anodic layer attains its glass-likesmoothness and resistance to abrasion and its great protection againstcorrosion. (M. Schenk, Werkstoif aluminum, Berne, 1948, p. 826.)According to the same author, it is necessary, finally, to subject thetreated aluminium goods to a polishing process to remove the depositwhich tarnishes the oxide layer and thus make it brilliant. This can bedone with a very soft wad of cloth not moving too quickly; in moreobstinate cases however, use has to be made of a thin polishing pastesuch as chrome green, alumina for polishing, etc.

Additives to the sealing baths have now been found which prevent theformation of this coating on the anodically oxidised sealed aluminium.In particular formaldehyde condensation products of aromatic sulphonicacids are suitable for this purpose insofar as they are capable ofeither dispersing or retaining in solution the basic pre cipitates whichoccur in the sealing bath. In this way, these precipitates are preventedfrom settling on the surface of the aluminium from which they have to beremoved by a further process. Aluminium treated according to this newmethod can be taken from the sealing bath, rinsed, and dried; itssurface is pure and is of a brilliancy which up to now could only beattained by the after-treatment mentioned above.

Example 500 g. of nickel acetate crystals, 100 g. of cobalt acetatecrystals and 800 g. of boric acid are dissolved in 100 litres of water;100 g. of the condensation product from naphthalene sulphonic acid andformaldehyde (produced for example according to U. S. Patent No.1,336,759) are added to this solution. The temperature of the bath nitedStates Patent O F 2,755,239 Patented July 17, 1956 is raised to 90100,the anodically oxidised, dyed or undyed aluminium is entered and thebath is kept for about 20 minutes either at the boil or almost boiling.The aluminum is then rinsed and dried. Its surface is as brilliant as itwas before the sealing operation. Polishing is unnecessary and does notincrease the brilliance of the surface at all.

It is not absolutely necessary to keep to the temperatures mentioned inthe above example, which temperatures correspond to those used inpractice today. It is not disadvantageous to work at lower temperatures.For example, temperatures around produce equally good, if not betterresults.

Condensation products from formaldehyde and naphthol sulphonic acids,formaldehyde and aromatic polysulphone sulphonic acids according toBritish Patent No. 683,084 can also be used instead of the condensationproduct from naphthalene sulphonic acid and formaldehyde mentioned inthe above example.

As it is known that the content of the sealing bath gradually becomespoorer, nickel and cobalt salts must be added from time ct time; this isalso true in the case of the formaldehyde condensation products whichare added.

What we claim is:

1. In a process for sealing the oxide coating of anodically oxidisedaluminium, the improvement which comprises subjecting the anodicallyoxidised aluminium to the action of a hot water sealing bath in thepresence in the bath of a water-soluble formaldehyde condensationprodnot of an aromatic sulphonic acid and of ions selected from thegroup consisting of nickel and cobalt ions.

2. In a process for sealing the oxide coating of anodically oxidisedaluminium, the improvement which comprises subjecting the anodicallyoxidised aluminium to the action of a hot water sealing bath in thepresence in the bath of a water-soluble formaldehyde condensationproduct of naphthalene sulphonic acid and of ions selected from thegroup consisting of nickel and cobalt ions.

Raub et 211.: Metal Industry, April 1940, pp. 206 and 207.

Raub et al.: Metal Finishing, August 1940, pp. 429 to 432.

1. IN A PROCESS FOR SEALING THE OXIDE COATING OF ANODICALLY OXIDISED ALUMINIUM, THE IMPROVEMENT WHICH COMPRISES SUBJECTING THE ANODICALLY OXIDISED ALUMINUM TO THE ACTION OF A HOT WATER SEALING BATH IN THE PRESENCE IN THE BATH OF WATER-SOLUBLE FORMALDEHYDE CONDENSATION PRODUCT OF AN AROMATIC SULPHONIC ACID AND OF IONS SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COLBALT IONS. 